In manufacturing semiconductor electronic components, an important step consists in treating a semiconductor substrate in a controlled atmosphere at very low pressure, e.g. for depositing layers of various materials by plasma deposition.
In industrial production, substrates in the form of wafers are conditioned and brought successively into a process chamber through an airlock or through a transfer chamber. In the process chamber, the atmosphere must be controlled very accurately, in particular to avoid the presence of any impurity or of any pollution.
Progress made in recent years in the semiconductor industry is essentially related to the increase in the integration of electronic circuits into components of a few square millimeters in area, defined on silicon wafers that are increasingly large.
Numerous (up to 400) technological steps are required to make such circuits, and, during the process, the pressure in the process chamber is subjected to sudden variations between various steps during which the pressure must be controlled and set to appropriate values.
Generating the low-pressure controlled-atmosphere in the process chamber requires the use of effective pumping systems. Such a system generally comprises a primary pump whose outlet is connected to atmosphere and whose inlet is connected to the outlet of a secondary pump such as a turbomolecular pump whose inlet is connected to the process chamber.
The process steps in the process chamber require the presence of special gases, and, by acting on the substrate, they generate gaseous compounds that must be removed. As a result, the pumping system must pump a variable atmosphere containing gaseous compounds that must be treated by gas treatment apparatus in order to deliver to atmosphere only compounds that are inoffensive.
Currently, pumping and gas treatment systems are situated remote from process chambers, i.e. they are connected to process chambers via long and costly pipes that are over ten meters long.
The reason behind that distance and those pipes is that current pumping and gas treatment systems are heavy and voluminous, and they give rise to adverse effects such as vibrations that it is essential to avoid in the process chamber.
Currently, an electronic component factory is therefore designed in a building having at least two levels, the upper level containing the process chamber(s), and the lower level containing the pumping and gas treatment apparatus. Pipes interconnect the two levels to convey the vacuum.
The pipes which are essential in known structures suffer from several drawbacks:
the pipes themselves generate vibrations;
the pipes constitute a large surface area on which the pumped gases can deposit in the form of particles; particles deposited in that way can backscatter from the pipe into the process chamber, thereby increasing the contamination of the chamber during subsequent steps of the process;
the pipes require major mechanical support means;
to reduce the deposits in the pipes, it is possible to provide temperature control, but such control is extremely costly and very difficult to implement;
a monitoring and control system that is complex to implement must be provided for reasons of safety in the event of leakage, since the pumped gases are harmful; and
the considerable amount of space needed requires large facilities and large floor areas for the factories; their cost is very high; losses from the cold line are non-negligible.